Dental furnace



T. M. DUDGEON.

DENTAL FURNACE.

v WITNESSES www?? m'INvEN-ron l wwM-A T. M. DUDGEON.

DENTAL FURNACE.

APPLICATION man JUNE 25.1919.

Patented Dec. 5, 1922.

2 SHEETS-SHEET 2.

Patented ec. 5, 1922.

THOMAS M. DUDGEON, OF AVALON BOROUGH, PENNSYLVANIA, ASSIGNOR TO THE SUPERIOR MANUFACTURING CGMPANY, OF PITTSBURGH, PENNSYLVANIA, A CORk PORATION 0F PENNSYLVANIA.

DENTAL FURNACE.

, Application mea June 25, 1919. seriai No. 306,558.

ToaZZ wlw/m t may concern.: p A l Be it known that 1, THOMAS; M. DUDGEON, a citizen of the United States, and residing in the borough of Avalon, in the county of Allegheny and State of Pennsylvania, have invented or discovered new and useful'lmprovements in 4Dental Furnaces, of which the following is a specification.

My invention consists in a furnace for the preparation of molds for dental castings.

The process of forming such molds is as follows. A piece of casting'wax is pressed and shape. v e applied the operation of evaporating the waxl down into the tooth cavity to take an accurate impression of the latter and the protruding portion of the wax is carved and shaped to produce the desired exterior con- Thus what is tour of the tooth when filled. termed the model is formed. The model is then mounted on the sprue, which is a short length of wire, andy painted with the investment material. The sprue is now mounted on the sprue holder or crucible former, and the flask or bucket set down on the sprue holder, surrounding the model. The flask is then filled with the investment material, thus embedding the model. The investment material is then allowed to set. Then the sprue holder is warmed and it and the sprue removed from the flask, leaving the hardened mass of investment material withV perature is excessive, the mold will be burned land the thin carbon skin which should cover the walls of the mold will be destroyed, leaving the walls of the mold cavity rough andv porous. lf the temperature is not sufficiently high or maintained for a sufficient period,

the wax will be incompletely evaporated and" the mold cavity will be of impropercapacity If -the vheat has been properly should be completed in approximately fortyve minutes. Where therwax has beenevappolishing.

over a gas flame, or burner, and it is quite y evident that constant watching and great skill is necessary to obtain evenlyv a fairly satisfactory mold.-

It hasv been estimated that in the case be ground and polished before they can be put in place in the tooth. n

The object which l have in view is'the provision of a furnace or apparatus for heating the flask and evaporating the wax model in such a manner that the mold will 'be perfect and an accurate negative of the model', l

with its walls lproperly coated with the carbon film. `I eifectthis objectby providing of the averageoper'ator approximatelyl 90% l of his fillings are either u nusablecr must so.A

means whereby the rise in temperature is sufficiently slow to avoidv the boiling orv steaming ofthe wax,"while in due time'theproper maximum temperature is attainedto thoroughly evaporate the wax without burning the' mold or injuring the carbon film which should coat its walls. But this temperature is never exceeded, so vthat the mold cannot be injured by leaving the flask overtime in the furnace.` The result is thatthe molds produced inmy improved furnace are perfect and the fillings subsequently' cast therein are ready for installation in the tooth ycavities without requiring any grinding'or Many other novel features of construction and arrangement of parts will appear from the lfollowing description. y

#In the accompanying drawings, which are merely intended to illustrate a practical embodiment of theprinciples of my invention in a furnacel wherein gas is used4 for fuel, and not to limit the scope ofthe former to 'the structure shown, Fig. 1 is `a perspective.

of the furnace; F ig. 42'- is a vertical section of the same;Fig. 3 is atop planview of the ioo @Ven Porti@ af .thffureavith Vtheta? .C10-g all preferably formed of metal or other suitable material.

rlhe base A consists of an open top box having perforated vertical walls 1 and door 2. The floor is provided with a protective layer 3 of heat insulating material, such as asbestos, and 4 represents air ports extending through said floor and asbestos sheet. The top edges of the walls 1 are turned inwardly in a horizontal planeand then ver-v tically, as shown more clearly .in F ig. 2, forming an L-shape flange to support the oven member.

5 are the angle shape legs secured to the exterior corners of the walls 1 and extending slightly above the same, as shown. Near their lower ends the legs 5 support the horizontal shelf 6 upon which is mounted the Bunsen burner D whose top extends up into the combustion chamber, as shown. 7 is the gas supply pipe leading under the shelf 6 to the burner D, and Vprovided witha regulating valve 8 provided with an indicating finger 9 which moves overa fixed dial 1()4 The combustion chamber is provided with a i lighting hole covered bythe swing plate 11.

r1`he oven B conforms in cross section to that of the combustion chamber', having vertical walls 12having an inturned bottom flange which fits into the L-shape iiange on the top of the combustion chamben the upper ends of the legs 5 assisting in holding the parts together. rlhe floor 1.3vis somewhat elevated and has a downwardly turned edge fiange whichrests on the bottom flange 4of the side walls of the oven. The floor is preferably riveted to the side walls. Above the floor the side walls are provided with: an

f ducts of combustion.

E is the removable oven liningmember which may be conveniently bent up of sheet metal in substantially the vform shown in Fig. 5, having vertical end walls 15 and rear wall 16 while lcorner braces or spacers 17fare formed by doubling the metal, and at the front the end walls are bent outward to form the flanges 18. The top edges of the `walls of the oven.

end and rear walls are inclined inwardly substantially parallel with the inclines of the Thus, when the oven lining is in position, as shown in Fig. 3 vertical flues are formed', in the ends and rear of the oven, into the bottoms of which open the ports 14 while the tops of thel flues are open and turn inward owing to the inclination of the top of the oven and oven lining walls. The spacers 17 extend into and fit the rear corners of the oven and the flanges 18 fit into the front corners of the same, thus ,holding the lining snugly in place.

The front wall of the oven is provided with a rectangular doorway7 19 which preferably extends across nearly the entire width of the oven, and is provided with an exterioriy mounted sliding door 2O provided with an internal lining of asbestos 21. c

One end wall 15 is provided with a circular aperture 22 which is alined with a similar aperture in the end wall of the oven,

F is a thermostatic device mounted in said vaperture in the oven wall, and is thus subau oven thermometer which will enable the oven heat to be read. 23 is the pointer working on the curved dial 24, and 25 is an arm rigid with or moving in unison with the pointer 23 and extending through a slot 26 out in a circumferential direction in the thermometer case.

The top closure C is of proper contour to fit down on the open top of the oven and form a dome for the fiues and oven compartment.

Thus, it is shown inthe form of a truncated pyramid having a depending flange 27 which slips down over the oven walls. r1`he throat 28 of the closure is preferably cylin* drical and provided with a fiap valve 29 hinged at one side, 30 is a lever extending rigidly from said flap valve for operating the same. rllhe outer end of said lever is bent to form a loop through which extends a link 31 whose lower end is pivotally attached to the arm25. 32is a pierced ball slipped on said link and resting onthe end of the lever 30. The upper end of the link 31 is threaded and provided with a thumb nut 33. 1t is evident that as-the temperature toward the right on the dial 24,the arm 25 will swing downwardly` drawing'down the link 31, and when the nut 33 strikes the vball 32, the lever 30 `will be drawn down and, as the temperature rises, the flap valve will be gradually opened. 1t is also evident that the heat from thecombustion chamber will pass upwardly through the flues into the interior of the top closure. Thus the ovenmwillbe uniformly heated at the bottom and sides,

yand will be automatically ventilated by means of the flap valve.

`of the oven rises, and the pointer 23 moves When a wax model is to be evaporated to form a mold, the flask containing the investment material and model, prepared as already described, is placed in the oven and its door closed. The valve 8 is now opened to the proper degree dictated bythe gas pressure in the pipe. The thumb nut 323 is adjusted so that the heating of the oven Will be gradual to avoid boiling or steaming the Wax. IThus I prefer to adjust the nut so that the Hap valve Will begin to open at an oven temperature of, say, 100 Fahr. Thus the heat Will rise more gradually. As the heat increases, the flap valve Will gradually open Wider to increase the ventilation and render the rise in oven temperature gradual. When the maximum temperature, approximately 320 Fahr. is attained, the flap valve should be open sufficiently to prevent any further substantial f increase in the internal heat of the oven. Thus the gas pressure must be taken into consideration, so that the proper amount of gas Will be supplied to the burner to furnish suiiicie'nt heating power Vto gradually raise the oven temperature to the maximum desired but not such an excess that the oven heat can be increased beyond the safe maxi mum. Thus when a furnace is installed the nut 33 should Vbe adjusted and the proper position of the gas valve determined, so that thereafter, When a Wax model is to be evaporated, the flaslrmay be inserted in the oven and the door closed, and then the gas valve opened to the degree found to be proper and the burner lighted.

Any other convenient heating agent than a gas burner, such, for instance, an electrical heater may be used.

The evaporation process usuallytalzeain my improved furnace, approximately fortyive minutes, during which time the oven` heat gradually reaches the maximum and maintains the same for a period sufficient to properly form themold. During the operation no care or attention is required, and therefore the dentist or other operator may give his undivided attention to other Work, and should he neglect to remove the. flask at the termination of the proper time, no injury will result, as the safe maximum temperature can not be exceeded and the mold will be found, when removed, in the same perfect condition as it had attained to at the end of the forty-fivev minutes.

it is thus evident thatno particular skill or experience is required, and as the furnace can be manufactured and sold at moderate cost and contains nothing liable to become impaired, a dentist With even a very limited practice will find it a valuable possession. In use, my invention has provedr itself very advantageous, the molds being ac-` curately formed With smooth carbon filmed 4 Walls, and the illing orcastings therefrom have iit properly into `spaces or cavities for Which they 'were intended Without preliminary grinding or polishing.

What Iy desire to claim is: i

l. In a dental furnace for the purposes described, ythe combination of a burner chamber, an outer casing superimposed von' said burner chamber and provided with an i intvardly contracted top,y an oven in said casing closed olf from the latter on its bottom and sides but having a top open to thel contracted portionk of said casing, heating means in said burner chamber,"a valve in the contracted top of said casing, and thermostatic means subjected `to the internal heat o-f said ovenand controlling said valve. l

of said oven member bent atV the back corners to form integrally connected flanges v vhereby verticalflues are formed connecting at their lower ends With said ports, a top dome closure removably mounted on said ovenmember into which the upper ends of said flues and of the false oven open, a valve for the throat of said dome, and thermostatic means actuated by the internal heat of` said oven controlling said valve.

Signed at Pittsburgh, Pa., this 20th day of June, 1919.

THOMAS M. nUDsEoN.y 

